1. Field of the Invention
The present invention relates to a camera provided with a zoom lens and, more particularly, to a zooming mechanism for the viewfinder optical system of the camera.
2. Description of the related art
Recently, a compact and light camera having a simple construction, provided with a zooming function, has become commercially available. The photographing and viewfinder optical systems of the camera are constructed as independent optical systems in this kind of camera, i.e., both optical systems are respectively provided with independent zooming mechanisms. Therefore, when, for example, the zooming of the photographing optical system is carried out, the zooming of the viewfinder optical system is synchronously made.
According to the zooming operations to be performed by the photographing optical system of a known camera provided with a zoom lens, when the zoom lens is simply moved by a motor, the back focal distance is varied since the lens is located at slightly different positions between a lens forward zooming operation and a lens backward zooming operation. This is because the mechanism for transmitting the force of the motor to the zoom lens includes some play such as backlash between the gears. Accordingly, in order to prevent the back focal distance from being varied between a lens forward zooming operation and a lens backward zooming operation, the zooming mechanism of the photographing optical system is designed such that a back focal distance amount obtained, for example, in an operation for moving a zoom lens forward, is set to a reference, and a back focal distance compensation is performed in an operation for moving the zoom lens backward. According to the known method for compensating the back focal distance, when an operation for moving the lens in the non-reference direction has been completed, a motor for driving a zoom barrel and, accordingly, the zoom lens, is reversed for a short period of time so as to move the zoom lens in an opposite direction, i.e., the zoom lens is moved slightly in the reference direction. The photographing and viewfinder optical systems are interlocked with each other, i.e., both optical systems are driven by the above-mentioned motor so as to equalize the variation of the magnification of the photographing optical system and that of the viewfinder optical system to each other. Therefore, when the movement of the zoom lens of the photographing optical system is reversed, the zoom lens of the viewfinder optical system is moved in association with the movement of the zoom lens of the photographing optical system. That is, when the back focal distance compensating operation is performed by the zoom lens of the photographing optical system, the condition of an image viewed through the viewfinder is slightly varied irrespective of or against the intention of a photographer. Thus, the photographer cannot reliably use the camera provided with the zoom lens.